Neural crest is a unique population of cells that migrate extensively during vertebrate embryogenesis. Of particular interest, cranial neural crest (CNC) cells migrate throughout the face to form most of the craniofacial skeleton. Defects in their proliferation, migration, or survival lead to numerous diseases and birth defects, including cleft lip/palate, Treacher-Collins syndrome, and DiGeorge syndrome. Despite recent progress in understanding aspects of neural crest development, the mechanisms underlying neural crest migration are still unclear. Thus, studying their migratory behavior and the regulation of actin cytoskeleton therein is crucial for understanding the basis of congenital craniofacial disorders. From a microarray screen, I have identified multiple actin cytoskeleton regulator (ACR) genes that are predominantly expressed in neural crest cells. My preliminary studies reveal that Myosin-X and Caldesmon are both critical for proper CNC cell migration via regulating cell morphology and membrane protrusions. Based on these findings, I hypothesis that neural crest cells achieve their unique migratory ability through specific ACRs to rapidly and precisely control their cytoskeletal dynamics. In this proposal, I will investigate the mechanism of neural crest migration by further analyzing the activities of these ACRs, and establishing their physical and functional interactions with actin structures. Specifically, I will combine classical embryology techniques with modern cell biology, biochemistry, and in vivo microscopy to study the dynamic arrangements of actin cytoskeleton during CNC migration and examine how ACRs in the neural crest regulate this process. Experiments will be carried out in frog and chick, taking into account the advantages of both model systems: simple gene and tissue manipulation in frog, and high-resolution imaging and late stage electroporation in chick. The following specific aims will be performed: 1) Examine the dynamics of actin cytoskeleton during normal neural crest migration by real time imaging. 2) Determine the role of Myosin-X and Caldesmon in regulating actin dynamics during CNC migration. 3) Functionally characterize Cdc42ep1 and additional candidate genes identified in the microarray screen for their roles in neural crest development. 4) Determine functional and physical interactions between ACRs in CNC migration.